Add Washington Paid Family and Medical Leave (WA PFML)

[daphnehanse11]

Closes #8136

Summary

Adds a Washington Paid Family and Medical Leave eligibility and maximum benefit calculator.

Given a Washington worker's earnings history and a selected leave scenario, the model returns:

• wa_pfml_eligible
• wa_pfml_weekly_benefit_amount
• wa_pfml_max_leave_weeks
• wa_pfml

wa_pfml is modeled as a maximum annual benefit estimate:
wa_pfml_weekly_benefit_amount × wa_pfml_max_leave_weeks

This PR does not model claimed leave or paid household income, so wa_pfml is not added to household_state_benefits.

Inputs

Core inputs:

• state_code
• weekly_hours_worked
• employment_income
• wa_pfml_leave_type

Supported leave types:

• FAMILY
• MEDICAL
• COMBINED
• MEDICAL_WITH_PREGNANCY_INCAPACITY
• COMBINED_WITH_PREGNANCY_INCAPACITY
• NONE

Optional accuracy overrides:

• wa_pfml_qualifying_period_hours_worked
• wa_pfml_average_weekly_wage_override

Statutory rules modeled

Eligibility — RCW 50A.15.010

• 820-hour qualifying-period threshold

Weekly benefit — RCW 50A.15.020(5)-(6)

• 90% replacement below 50% of SAWW
• 90% of the first 50% of SAWW plus 50% above that threshold
• minimum $100/week, or AWW if AWW < $100
• maximum 90% of SAWW
• AWW and benefit rounded down to the next lower dollar

Duration — RCW 50A.15.020(3)

• family leave: 12 weeks
• medical leave: 12 weeks
• combined leave: 16 weeks
• medical leave with pregnancy incapacity: 14 weeks
• combined leave with pregnancy incapacity: 18 weeks

Program values use Washington's published SAWW and maximum weekly benefit amounts through 2026.

Current simplifications

• If wa_pfml_qualifying_period_hours_worked is not provided, eligibility uses the proxy weekly_hours_worked * 52.
• If wa_pfml_average_weekly_wage_override is not provided, average weekly wage uses the proxy floor(employment_income / 52).
• The model estimates maximum leave and benefit for a selected leave type; it does not infer whether a factual life event qualifies as family vs. medical leave.

Tests

Adds WA PFML coverage for:

• weekly benefit calculation
• eligibility
• maximum leave weeks
• integrated maximum annual benefit

30 WA PFML YAML tests pass locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (20705b0) to head (1212555).
⚠️ Report is 34 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##             main     #8138       +/-   ##
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+ Coverage   85.36%   100.00%   +14.63%     
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  Files           3         8        +5     
  Lines          41       116       +75     
  Branches        2         0        -2     
============================================
+ Hits           35       116       +81     
+ Misses          6         0        -6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+14.63%)	⬆️

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